This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-160510, filed May 30, 2000; and No. 2000-251158, filed Aug. 22, 2000, the entire contents of which are incorporated herein by reference.
This invention relates to a method of manufacturing a synthesis gas to be employed for the synthesis of gasoline, kerosene and gas oil by way of the Fisher-Tropsch reaction system.
Japanese Patent Unexamined Publication No. 6-184559 discloses a method of synthesizing gasoline, etc. wherein a synthesis gas containing hydrogen (H2) and carbon monoxide (CO) is manufactured at first from natural gas, and this synthesis gas is then employed for synthesizing gasoline, etc. by way of a GTL (Gas to Liquid) process according to the Fisher-Tropsch reaction system. In this method, natural gas containing methane as a main component is introduced together with steam into a reformer provided with a reforming catalyst, and the reformer is heated up to a predetermined temperature to allow mainly hydrocarbons contained in the natural gas to react with the steam, thereby manufacturing the synthesis gas.
However, since the composition of synthesis gas produced by this method is constituted by H2:CO:CO2=5:1:0.5 (molar ratio), the content of hydrogen gas becomes surplus for the synthesis of gasoline, etc. Namely, in the Fisher-Tropsch reaction system where a cobalt catalyst is employed, an optimum molar ratio between H2/CO is 2. Whereas, when an iron catalyst is employed in the Fisher-Tropsch reaction system, an optimum molar ratio between H2/CO is 1 to 2.
Under the circumstances, there is disclosed in FIGS. 3 and 4 of Japanese Patent Unexamined Publication No. 6-184559 a reaction system for manufacturing a synthesis gas, which comprises a reformer system consisting of a convection reformer, a self-heating reformer (a partial oxidation furnace) and a convection reformer heater; a carbon dioxide stripper disposed on a downstream side of the reformer system; and a Fisher-Tropsch reactor disposed on a downstream side of the carbon dioxide stripper.
According to this reaction system, the convection reformer is heated by making use of heat generated from the convection reformer heater, and then, a natural gas mixed together with steam is fed together with carbon dioxide that has been separated and recovered from a synthesis gas (to be explained hereinafter) to the convection reformer, thereby allowing part of mainly methane of the natural gas and the carbon dioxide to be reacted with the steam, thus performing a reforming reaction. Thereafter, the resultant reformed gas, the natural gas and oxygen are fed to the self-heating reformer to cause mainly hydrogen gas contained in the reformed gas to burn so as to heat the gaseous mixture up to a temperature which is suited for the reaction between mainly methane contained in the reformed gas and the steam, thereby generating a synthesis gas.
The heat of this synthesis gas is then recovered at the convection reformer heater, thereby enabling the heat to be utilized a heating source for the convection reformer. The synthesis gas after it has been subjected to the aforementioned heat recovery is then fed to the carbon dioxide stripper in which carbon dioxide contained in the synthesis gas is separated and removed from the synthesis gas so as to obtain a gas having a predetermined molar ratio of CO/H2, the resultant gas being subsequently fed to the Fisher-Tropsch reactor. Part of carbon dioxide that has been recovered is allowed to be mixed with the natural gas at a location on an upstream side of the convection reformer, and the rest of the carbon dioxide is allowed to be discharged outside the system.
However, the invention disclosed in the aforementioned Japanese Patent Unexamined Publication No. 6-184559 is accompanied with a problem that since the convection reformer is heated by making use of the heat from the convection reformer heater, only an insufficient quantity of heat is available for reforming the aforementioned steam-containing natural gas at the convection reformer, so that only part of methane in the natural gas can be reformed. Because of this, the reformed gas from the convection reformer is fed to the self-heating reformer (a partial oxidation furnace) so as to cause the hydrogen gas in the reformed gas to burn using the oxygen that has been fed to the self-heating reformer, thereby heating the gaseous mixture up to a temperature required for generating a predetermined synthesis gas.
As a result, a large quantity of oxygen is required to be fed to the self-heating reformer. Since oxygen is generally produced in an oxygen plant where oxygen is isolated from air atmosphere through a low temperature treatment, the employment of a large quantity of oxygen leads not only to the consumption of enormous quantity of energy but also to an increase in scale of plant, thereby increasing the manufacturing cost of the synthesis gas.
On the other hand, there is also disclosed a method of manufacturing a synthesis gas in xe2x80x9cChemical Engineering Progressxe2x80x9d, Wang; August 1987, pp.46-53. More specifically, the production of oxoalcohol through a reaction of olefin with a mixed gas comprising hydrogen and carbon monoxide at a ratio of H2/CO=1 to 2 is described in the left column page 49 of the publication.
This publication also discloses the manufacture of synthesis gas containing hydrogen and carbon monoxide at a ratio of H2/CO=1 to 2 in the right column page 49 of the publication as Method 4A wherein, on the occasion of feeding a desulfurized natural gas to the steam reformer, carbon monoxide is added from outside the system (for example, from a neighboring ammonia plant) to the natural gas so as to allow a reaction to take place among the natural gas, steam and carbon dioxide. Although this method is advantageous for the reason that the production of hydrogen in an excessive ratio can be minimized without necessitating the addition of oxygen as described in the right column lines 8-11 page 49 of the publication, this method is disadvantageous mainly because it requires a CO2 source (for example, a neighboring ammonia plant). Therefore, the aforementioned Method 4A is useless except where a CO2 source such as an ammonia plant is located in the neighborhood.
Therefore, an object of this invention is to provide a method for manufacturing a synthesis gas, which makes it possible to procure CO2 inside a synthesis gas-manufacturing plant utilizing the Fisher-Tropsch reaction system, thereby enabling the synthesis gas to be cheaply manufactured by way of the Fisher-Tropsch reaction system without being restricted by the location of CO2 gas source such as an ammonia plant, the synthesis gas containing hydrogen gas and carbon monoxide at a molar ratio of H2/CO which is suited for synthesizing gasoline, kerosene and gas oil.
Another object of this invention is to provide a method of manufacturing a synthesis gas comprising hydrogen gas and carbon monoxide at a molar ratio of H2/CO which is suited for synthesizing gasoline, kerosene and gas oil by way of the Fisher-Tropsch reaction system, wherein a carbon dioxide-containing natural gas is fed to a reformer and then the resultant reformed gas is introduced from the reformer into the partial oxidation furnace so as to allow hydrogen in the reformed gas to burn through a reaction thereof with oxygen that has been fed to the partial oxidation furnace, the method being featured in that it is capable of minimizing the quantity of feeding oxygen to the partial oxidation furnace thereby making it possible to miniaturize an oxygen plant for producing oxygen.
Namely, this invention provides a method of manufacturing a synthesis gas containing CO and H2, which is suited for use in synthesizing gasoline, kerosene and gas oil by way of the Fisher-Tropsch reaction system; the method comprising the steps of;
feeding a steam-mixed natural gas to a reformer which is provided with a combustion radiation portion for burning a fuel, the reformer being designed to be heated by the combustion radiation portion;
recovering carbon dioxide from a combustion exhaust gas generated at the combustion radiation portion; and
adding the carbon dioxide to the steam-mixed natural gas at a location on an upstream side of the reformer, thereby allowing a reforming reaction to take place to obtain a synthesis gas containing CO and H2 at a molar ratio of H2/CO=1 to 2.5, which is suited for use in synthesizing gasoline, kerosene and gas oil.
In the method of manufacturing a synthesis gas according to this invention, carbon dioxide may be recovered from the synthesis gas produced in the reformer, the resultant carbon dioxide being allowed to recirculate in a region on an upstream side of the reformer.
In the method of manufacturing a synthesis gas according to this invention, the process of recovering carbon dioxide from the synthesis gas may be performed by making use of the same absorbent solution as employed in the process of recovering carbon dioxide from the combustion exhaust gas employed for heating the reformer. The process of recovering carbon dioxide from the synthesis gas may be performed using an amine-based absorption solution or a potassium carbonate-based absorption solution, while the process of recovering carbon dioxide from the combustion exhaust gas may be performed using alkanol amine which is minimal in deterioration other than monoethanol amine absorbent solution which is conventionally employed.
In the method of manufacturing a synthesis gas according to this invention, a preliminary reformer may be arranged at an upstream of the reformer, the natural gas to which steam has been added is supplied to the reformer via the preliminary reformer, the carbon dioxide recovered from the combustion exhaust is fed to a passageway connecting the reformer and the preliminary reformer.
In the method of manufacturing a synthesis gas according to this invention, the step of adding the carbon dioxide to the steam-mixed natural gas may be performed by arranging a moistening device at a posterior stage of the reformer, introducing a synthesis gas from the reformer into the moistening device, heating the moistening device with waste heat of the synthesis gas, feeding natural gas and water to the moistening device, and adding steam to the natural gas in the moistening device.
In the method of manufacturing a synthesis gas according to this invention, a purging gas containing carbon dioxide may be circulated in a region on an upstream side of the reformer, the purging gas is produced in the Fisher-Tropsch reaction system on the occasion of synthesizing gasoline, kerosene and gas oil by way of the Fisher-Tropsch reaction system by making use of a synthesis gas produced in the reformer.
This invention also provides an alternative method of manufacturing a synthesis gas containing CO and H2, which is suited for use in synthesizing gasoline, kerosene and gas oil by way of the Fisher-Tropsch reaction system; the method comprising the steps of;
feeding a steam-mixed natural gas to a reformer which is provided with a combustion radiation portion for burning a fuel, the reformer being designed to be heated by the combustion radiation portion;
recovering carbon dioxide from a combustion exhaust gas generated at the combustion radiation portion;
adding the carbon dioxide to the steam-mixed natural gas at a location on an upstream side of the reformer, thereby allowing a reforming reaction to take place; and
introducing a reformed gas from the reformer into a partial oxidation furnace simultaneous with an introduction of oxygen into the partial oxidation furnace, thereby allowing the reformed gas to react with the oxygen to obtain a synthesis gas comprising Co and H2 at a molar ratio of H2/CO=1 to 2.5, which is suited for use in synthesizing gasoline, kerosene and gas oil.
In this alternative method of manufacturing a synthesis gas according to this invention, carbon dioxide may be recovered from the synthesis gas produced in the partial oxidation furnace, the resultant carbon dioxide being allowed to recirculate in a region on an upstream side of the reformer.
In this alternative method of manufacturing a synthesis gas according to this invention, the process of recovering carbon dioxide from the synthesis gas may be performed by making use of the same absorbent solution as employed in the process of recovering carbon dioxide from the combustion exhaust gas discharged from the combustion radiation portion of the reformer. The process of recovering carbon dioxide from the synthesis gas may be performed using an amine-based absorption solution or a potassium carbonate-based absorption solution, while the process of recovering carbon dioxide from the combustion exhaust gas may be performed using alkanol amine which is minimal in deterioration other than monoethanol amine absorbent solution which is conventionally employed.
In this alternative method of manufacturing a synthesis gas according to this invention, a preliminary reformer may be arranged at an upstream of the reformer, the natural gas to which steam has been added is supplied to the reformer via the preliminary reformer, the carbon dioxide recovered from the combustion exhaust is fed to a passageway connecting the reformer and the preliminary reformer.
In this alternative method of manufacturing a synthesis gas according to this invention, the step of adding the carbon dioxide to the steam-mixed natural gas may be performed by arranging a moistening device at a posterior stage of the reformer, introducing a synthesis gas from the reformer into the moistening device, heating the moistening device with waste heat of the synthesis gas, feeding natural gas and water to the moistening device, and adding steam to the natural gas in the moistening device.
In this alternative method of manufacturing a synthesis gas according to this invention, it is preferable to feed a carbon dioxide-mixed oxygen to the partial oxidation furnace. Further, steam may be fed to the partial oxidation furnace.
In this alternative method of manufacturing a synthesis gas according to this invention, a purging gas containing carbon dioxide may be circulated in a region on an upstream side of the reformer, the purging gas is produced in the Fisher-Tropsch reaction system on the occasion of synthesizing gasoline, kerosene and gas oil by way of the Fisher-Tropsch reaction system by making use of a synthesis gas produced in the partial oxidation furnace.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.